furnace/src/engine/fileOps/tfm.cpp

/**
 * Furnace Tracker - multi-system chiptune tracker
 * Copyright (C) 2021-2024 tildearrow and contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "fileOpsCommon.h"

class TFMRLEReader;

struct TFMEndOfFileException {
  TFMRLEReader* reader;
  size_t finalSize;
  TFMEndOfFileException(TFMRLEReader* r, size_t fs):
    reader(r),
    finalSize(fs) {}
};


class TFMRLEReader {
  const unsigned char* buf;
  size_t len;
  size_t curSeek;
  bool inTag;
  int tagLenLeft;
  char tagChar;

  void decodeRLE(char prevChar) {
    int lenShift=0;
    tagLenLeft=0;
    char rleTag=0;
    do {
      rleTag=readC();
      tagLenLeft|=(rleTag&0x7F)<<lenShift;
      lenShift++;
      // sync back since we've already read one character
      tagLenLeft--;
    } while (!(rleTag&0x80));
    inTag=true;
    tagChar=prevChar;
  }

public:
  TFMRLEReader(const void* b, size_t l) :
    buf((const unsigned char*)b),
    len(l),
    curSeek(0),
    inTag(false),
    tagLenLeft(0),
    tagChar(0) {}

  // these functions may throw TFMEndOfFileException
  unsigned char readC() {
    if (curSeek>len) throw TFMEndOfFileException(this, len);
    if (inTag) {
      if (!tagLenLeft) {
        inTag=false;
        return readC();
      }
      tagLenLeft--;
      logD("one char RLE decompressed, tag left: %d, char: %d", tagLenLeft, tagChar);
      return tagChar;
    }

    unsigned char ret=buf[curSeek++];

    // MISLEADING DOCUMENTATION: while TFM music maker's documentation says if the next byte
    // is zero, then it's not a tag but just 0x80 (for example: 0x00 0x80 0x00 = 0x00 0x80)
    // this is actually wrong
    // through research and experimentation, there are times that TFM music maker
    // will use 0x80 0x00 for actual tags (for example: 0x00 0x80 0x00 0x84 = 512 times 0x00
    // in certain parts of the header and footer)
    // TFM music maker actually uses double 0x80 to escape the 0x80
    // for example: 0xDA 0x80 0x80 0x00 0x23 = 0xDA 0x80 0x00 0x23)
    if (ret==0x80 && curSeek+1<len) {
      if (buf[curSeek+1]!=0x80) {
        decodeRLE(buf[curSeek-2]);
        tagLenLeft--;
        return tagChar;
      } else {
        // to avoid outputting the extra 0x80
        curSeek++;
        return ret;
      }
    }
    return ret;
  }

  char readCNoRLE() {
    if (curSeek+1>len) throw TFMEndOfFileException(this, len);
    return buf[curSeek++];
  }

  void read(unsigned char* b, size_t l) {
    int i=0;
    while(l--) {
      b[i++]=readC();
    }
  }

  void readNoRLE(unsigned char *b, size_t l) {
    int i=0;
    while (l--) {
      b[i++]=buf[curSeek++];
      if (curSeek>len) throw TFMEndOfFileException(this, len);
    }
  }

  short readS() {
    return readC()|readC()<<8;
  }

  short readSNoRLE() {
    if (curSeek+2>len) throw TFMEndOfFileException(this, len);
    short ret=buf[curSeek]|buf[curSeek+1]<<8;
    curSeek+=2;
    return ret;
  }
};

String TFMparseDate(short date) {
  return fmt::sprintf("%02d.%02d.%02d", date>>11, (date>>7)&0xF, date&0x7F);
}

bool DivEngine::loadTFM(unsigned char* file, size_t len) {
  struct InvalidHeaderException {};
  bool success=false;
  TFMRLEReader reader=TFMRLEReader(file, len);

  try {
    DivSong ds;
    ds.systemName="Sega Genesis/Mega Drive or TurboSound FM";
    ds.subsong[0]->hz=50;
    ds.systemLen = 1;
    ds.system[0]=DIV_SYSTEM_YM2612;

    unsigned char magic[8]={0};

    reader.readNoRLE(magic, 8);
    if (memcmp(magic,DIV_TFM_MAGIC,8)!=0) throw InvalidHeaderException();

    unsigned char speedEven=reader.readCNoRLE();
    unsigned char speedOdd=reader.readCNoRLE();
    unsigned char interleaveFactor=reader.readCNoRLE();

    // TODO: due to limitations with the groove pattern, only interleave factors up to 8
    // are allowed in furnace
    if (interleaveFactor>8) {
      logW("interleave factor is bigger than 8, speed information may be inaccurate");
      interleaveFactor=8;
    }

    if (speedEven==speedOdd) {
      ds.subsong[0]->speeds.val[0]=speedEven;
      ds.subsong[0]->speeds.len=1;
    } else {
      for (int i=0; i<interleaveFactor; i++) {
        ds.subsong[0]->speeds.val[i]=speedEven;
        ds.subsong[0]->speeds.val[i+interleaveFactor]=speedOdd;
      }
      ds.subsong[0]->speeds.len=interleaveFactor*2;
    }
    ds.subsong[0]->ordersLen=reader.readCNoRLE();

    // order loop position, unused
    (void)reader.readCNoRLE();

    ds.createdDate=TFMparseDate(reader.readSNoRLE());
    ds.revisionDate=TFMparseDate(reader.readSNoRLE());

    // TODO: use this for something, number of saves
    (void)reader.readSNoRLE();

    unsigned char buffer[384];

    // author
    logD("parsing author");
    reader.read(buffer,64);
    ds.author=String((const char*)buffer,strnlen((const char*)buffer,64));
    memset(buffer, 0, 64);

    // name
    logD("parsing name");
    reader.read(buffer,64);
    ds.name=String((const char*)buffer,strnlen((const char*)buffer,64));
    memset(buffer, 0, 64);

    // notes
    logD("parsing notes");
    reader.read(buffer, 384);
    String notes((const char*)buffer,strnlen((const char*)buffer,384));

    // fix \r\n to \n
    for (auto& c : notes) {
      if (c=='\r') {
        notes.erase(c,1);
      }
    }

    ds.notes=notes;
    BUSY_BEGIN_SOFT;
    saveLock.lock();
    song.unload();
    song=ds;
    changeSong(0);
    recalcChans();
    saveLock.unlock();
    BUSY_END;
    success=true;
  } catch(TFMEndOfFileException& e) {
    lastError="incomplete file!";
  } catch(InvalidHeaderException& e) {
    lastError="invalid info header!";
  }

  return success;
}